Stress Engineering in Developing Mixed Conducting Si-Ge Solutions for Lithium Ion Batteries

Despite having the highest theoretical specific capacity (3579 mAh/g), silicon has been known to undergo massive anisotropic volume expansion (~280%), and consequently, causing the fracture of the particles and loss of the specific capacity upon further cycling. Germanium has been reported to undergo isotropic expansion and observed in the in-situ studies to sustain lithiation induced fracture up to the particle size of ~680 nm. In this work, solid solution of Si and Ge of various compositions were synthesized. The formation of a single phase solid solution was confirmed by the X-ray diffraction and the electrode morphology were studied using Scanning electron microscopy.  The solid solution of equimolar Si and Ge (Si_0.5Ge_0.5) displayed excellent electrochemical performance both in the cyclic stability as well as the total specific capacity.